Soluble rhodium complexes containing coordinated chiral phosphines catalyze the hydrogenation of prochiral olefins to give optically active alkane derivatives (Knowles et al. U.S. Pat. No. 3,849,840). Particularly useful are hydrogenations of prochiral enamides to form an excess of one enantiomer of a chiral N-acyl amine derivative (Knowles et al. U.S. Pat. No. 4,005,127 and 4,008,281; Kagan et al. U.S. Pat. No. 3,798,241; Aviron-Violet U.S. Pat. No. 3,949,000), i.e., ##STR1## wherein the above R groups may be alkyl, cycloalkyl or aryl, etc. These hydrogenations result in the formation of chiral natural products and substances useful as flavorings and pharmaceuticals.
Asymmetric hydrogenation, per se, has been widely studied as evidenced by the following review articles:
Kagan, Pure Appl. Chem., 43 401 (1975);
Scott et al., Science, 184, 943 (1974);
Birch et al., Organic Reactions 24, 1 (1976); and
Marko et al., Catal. Rev., 8, 219 (1973).
Catalysts for these hydrogenations are typically prepared by combining some suitable Group VIIIb metal olefin complex starting material, preferably rhodium, e.g., .mu..mu.'-dichloro-bis-(1,5-cyclooctadiene rhodium), with the desired chiral phosphine. Depending on the circumstances, the rhodium phosphine complex thus formed is either isolated or a solution thereof is used directly to catalyze hydrogenations.
The foregoing procedures are generally satisfactory. However, in other instances these procedures are difficult and, at best, inconvenient because of problems encountered in isolation and purification of the phosphine component of the catalyst, e.g., when the phosphine is an oil and/or air-sensitive.
The chiral chelating bis-phosphine (4R,5R)-trans-4,5-bis-(di-3-tolylphosphinomethyl)-2,2-dimethyl-1,3-dioxola ne (3-tolyl DIOP) is useful in forming rhodium complex catalysts for enantioselective hydrogenations of enamides (Kagan et al., J. Organometal Chem., 91, 105 [1975]). The utility of this phosphine and similar such substances in like applications is severely limited by the fact that this phosphine is an oil and thus is difficult to isolate contamination-free other than by tedious chromatographic purification techniques.
It is an object of this invention to provide an improved method for the obtention of rhodium complex catalyst compositions containing (4R,5R)-trans-4,5-bis-(di-3-tolylphosphinomethyl)-2,2-dimethyl-1,3-dioxola ne and related diphosphines.